1. Technical Field
The present invention relates to a tool path display apparatus having a display unit for the acceleration or jerk of a tool tip point.
2. Description of Related Arts
Some of the numerical control apparatuses that are currently used to control machine tools have a function for displaying a position command path and a function for displaying the path on which a tool has actually moved. To be more specific, the coordinates of the tip point of a tool are calculated and displayed, from time series data of commanded positions and/or time series data of the actual positions of the drive axes of a machine tool. By this means, the shape error between the commanded path and the actual path of the tool tip point is visually analyzed.
As an example of such related arts, Japanese Patent No. 4648471 discloses calculating the three-dimensional coordinates of the tip part of a tool based on position information of the drive axes of a machine tool at each time, and information of the mechanical structure of the machine tool, and determining its path. Furthermore, Japanese Patent No. 4648471 discloses associating the path of a tool tip point and the accelerations of the drive axes of a machine tool and displaying them.
Furthermore, Japanese Patent No. 3517909 discloses displaying the acceleration of a tool feed axis, which is calculated from shape data of a workpiece, in the form of a graph, and determining corrected workpiece shape data by correcting an acceleration that is a singularity, equal to or above an acceleration threshold, to be equal to or below the threshold.
Furthermore, Japanese Patent Application Publication No. 2009-98982 discloses accurately simulating the path of a tool and/or the velocity of movement of the tool, prior to processing, and displaying the velocity, acceleration and jerk on a simulated tool path.
Incidentally, upon processing a workpiece with a machine tool, in order to have a desired machined surface on the workpiece, it is necessary to reduce the shape error of the actual position of a drive axis or a tool against the commanded position. Then, in order to analyze the cause resulting in the shape error, additional information such as acceleration, etc., is necessary, in addition to position information.
In particular, in the event a workpiece includes many curved surfaces, depending on the velocity at which a tool moves on the curved surfaces, the tangential acceleration and the normal acceleration also change. Consequently, the force that is applied from the tool to the machined surface of the workpiece also changes in accordance with such a change in acceleration. Then, the force that is applied to the machined surface influences the external appearance (stripe patterns, scratches, etc.) of the workpiece. Consequently, in order to analyze the shape error, physical information such as the acceleration and jerk of a drive axis or a tool is required.
Furthermore, according to the technique of Japanese Patent No. 4648471, it is necessary to check the acceleration of each drive axis separately, and it is therefore difficult to understand the association between acceleration and the machined surface visually. Also, acceleration according to Japanese Patent No. 3517909 is used to extract a singularity to equal or exceed a threshold, and therefore Japanese Patent No. 3517909 does not calculate acceleration in order to analyze shape error.
Furthermore, although Japanese Patent Application Publication No. 2009-98982 discloses displaying acceleration on a simulated tool path, Japanese Patent Application Publication No. 2009-98982 does not disclose displaying acceleration and so on, on the actual tool path. Consequently, with Japanese Patent Application Publication No. 2009-98982, it is not possible to analyze shape error in association with the actual machined surface.
The present invention has been made in view of the above backgrounds, and it is therefore an object of the present invention to provide a tool path display apparatus, which can easily analyze the shape error of the actual position of a drive axis or a tool, against the commanded position, and reduce the defects in the external appearance of a workpiece.